This invention relates to turbochargers for supplying relatively high pressure charge air to an internal combustion engine. More specifically, this invention relates to a turbocharger control actuator designed for improving engine efficiency during steady state cruise or part load operation, while at the same time providing protection against turbocharger overboost.
Turbochargers in general are well known in the art, and typically comprise a turbine wheel and a compressor wheel mounted on a common shaft and carried within isolated turbine and compressor housings. The turbine housing includes a gas inlet and a gas outlet, and is coupled to the exhaust gas manifold of a combustion engine for circulation of the exhaust gases through the turbine housing to rotatably drive the turbine wheel. In turn, the turbine wheel rotatably drives the compressor wheel which compresses ambient air and supplies the resultant so-called compressed charge air to the intake manifold of the engine. Importantly, in a vehicle application, the gas outlet of the turbine housing typically is coupled to exhaust system conduits which may include pollution and/or noise abatement equipment.
The use of turbocharged engines is highly advantageous when compared with conventional naturally aspirated engines in that substantially higher density fuel-air mixtures may be delivered to the combustion chamber or cylinders of the engine. This increased fuel-air density results in substantially improved engine performance and efficiency. However, with many internal combustion engines, it is desirable to limit the maximum pressure or boost pressure at which charge air may be delivered to the engine at full load engine operating conditions. That is, many turbochargers are capable of delivering charge air to the engine at a boost pressure substantially greater than the engine or the turbocharger can withstand. Accordingly, a wide variety of valves and other pressure control devices have been proposed to limit the maximum boost pressure of charge air supplied by the turbocharger compressor.
Turbocharger boost controls typically comprise controlled valve arrangements for bleeding off a portion of the compressed charge air, or alternately, for opening a bypass flow path around the turbine wheel for bypass of a portion of the engine exhaust gases out of driving communication with the turbine wheel. This latter arrangement utilizes a so-called waste gate valve controllable for limiting the maximum allowable rotational speed of the turbine wheel in order to limit correspondingly the maximum allowable rotational speed of the compressor wheel, and thereby limit the maximum boost pressure of the charge air supplied to the engine. Structurally, these waste gate valve arrangements include a control actuator responsive to engine or turbocharger parameters to control opening and closing of the waste gate valve. These control actuators are available in a variety of specific constructions and can be made responsive to any of a selected number or combination of parameters, such as compressor inlet pressure, compressor discharge pressure, turbine inlet pressure, or the like. For example, many actuators are available including a pressure-responsive diaphragm for controlling the position of the waste gate valve. In some designs, a spring biases the valve to a closed position preventing bypass of exhaust gases around the turbine wheel until compressor discharge pressure reaches a predetermined magnitude. See, for example, U.S. Pat. Nos. 1,310,683; 2,480,621; 2,878,797; 3,035,408; 3,195,805; 3,421,314; 3,931,712; and 4,005,579. Other designs utilize a spring to bias the valve to an open position, and couple the valve to a diaphragm responsive to parameter-indicative pressures to maintain the valve closed against the spring bias until compressor discharge pressure reaches a predetermined magnitude. See, for example, U.S. Pat. Nos. 2,374,708; 3,089,304; 3,102,382; 3,104,520; 3,233,403; 3,257,796; 3,611,711; and 4,005,578.
In these various diaphragm-controlled pressure responsive waste gate valve arrangements of the prior art, the waste gate valve in maintained in a closed position preventing bypass of exhaust gases around the turbine wheel whenever compressor discharge pressure is at or below the predetermined maximum allowable magnitude. This is desirable during substantially full load, transient operation such as acceleration in that the exhaust gases drivingly rotate the turbine wheel so that the turbocharger develops substantial boost pressure. However, during part load steady state cruise operation of the engine, substantial turbocharger boost pressure is not required, and it is therefore desirable to open the turbocharger waste gate valve to unload the turbocharger from the engine. That is, it is desirable during this part load condition to bypass exhaust gases around the turbine wheel to reduce back-pressure on the engine, and thereby correspondingly improve engine efficiency and economy. However, in the prior art, control actuators for controlling the position of a waste gate valve have not been designed for the dual purpose of preventing turbocharger overboost, as well as for opening the waste gate valve during part load cruise operation.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved turbocharger control actuator for opening a turbocharger waste gate valve during part load operation, and whenever compressor boost pressure reaches a predetermined maximum value.